The present invention relates to a control device for a motor vehicle occupant safety apparatus and, more responsive to longitudinal and/or transverse acceleration.
Control devices for the triggering of air bags, roll-over bars and the like are generally known. They respond when the measured acceleration exceeds the limit which is customary during a noncritical operation of the motor vehicle. The values involved may be absolute values or the duration of the measured acceleration as well as combinations of values and duration of this acceleration.
However, in the case of these known control devices, the safety device is, as a rule, not triggered when the motor vehicle is in a particularly critical condition. This critical condition will occur when the motor vehicle loses contact with the road by, for example, crashing downward.
The present invention is based on an object of providing a control device which triggers the occupant safety device particularly when the motor vehicle is in a particularly critical situation.
The invention achieves this object by providing an additional moving-condition sensor to trigger the safety apparatus independently of the acceleration sensor when the motor vehicle approaches a weightless condition.
In the case of weightlessness, such as arises from free fall the acceleration values in the motor vehicle are relatively low. Nevertheless, the safety device must already be triggered during the free fall since extremely high acceleration values frequent occur at the end of the weightless condition (impact). The present invention that the safety device to become operative already during the weightless condition in order to thus provide a sufficient protection for the vehicle occupants at the end of the weightlessness condition.
Since a condition of the motor vehicle which approaches weightlessness occasionally occurs during the normal driving operation, a further feature of the present invention differentiates between such "normal" and "critical" situations. In order to avoid an unnecessary triggering of the safety device in situations of this type which occur, for example, when driving over a hilltop, the duration of the critical condition is determined by a time function element. When this duration is short, that is, the critical condition is very brief with respect to time, the occupant safety device is not triggered. The circuit devices required for achieving this feature of the invention include connecting a time-function element behind the moving-condition sensor.
During the condition of weightlessness, a distance measuring sensor determines a distance from the ground which is clearly above the normal value. During the weightless condition, the sensor furnishes a value close to zero. Finally, the rebound of one or several of the vehicle wheels, when it is equal to the maximally possible value, is also a good indication of the condition of weightlessness.
Although a safety device for a roll-over bar of a motor vehicle is known from German Patent Document DE-PS 35 45 874 which is controlled by a rebound sensor, in contrast to the present invention, the free fall condition is not taken into account because the signal of the wheel rebound sensor will only have an effect when a tilt switch responds at the same time which is actuated when a certain tilt is exceeded. However, during the weightless condition, there is frequently no functional connection with the tilt of the vehicle.